1. Field of the Invention
The invention relates to a polymerizable liquid crystal compound, a liquid crystal composition including the compound and a polymer of the compound or the liquid crystal composition including the compound.
2. Related Art
A polymerizable liquid crystal compound has recently been utilized for an optically anisotropic substance such as a polarizing plate and an optical retardation plate. This is because the compound exhibits optical anisotropy in the liquid crystal state and then the liquid crystal molecules in this state are fixed fixed by polymerization. The kinds of optical characteristics required for a polymer having optical anisotropy depends on a purpose for use, and a compound having characteristics that suits the purpose is necessary. In the compound used for such a purpose, characteristics regarding its polymer are important in addition to the characteristic of optical anisotropy. The characteristics of the polymer include the rate of polymerization, transparency, mechanical strength, applicability, solubility, the degree of crystallinity, shrinkage, water permeability, water absorptivity, melting points, glass transition temperature, clearing points, chemical resistance and thermal resistance.
A compound having an acryloyloxy group as a polymerizable group among polymerizable liquid crystal compounds is used for such purposes (patent document Nos. 1 and 2). The acrylate has a high reactivity and the polymer derived from it has a high transparency. However, it is necessary to carry out the reaction in an atmosphere of an inert gas and to increase energy of ultraviolet irradiation, because the mode of polymerization is radical polymerization. Thus, an improvement of workability on curing in air and also of characteristics such as heat resistance, shrinkage, adhesive properties, adhesion and mechanical strength is required. Furthermore, a polymerizable liquid crystal compound (or its composition) is used for ink that is diluted with an organic solvent for the purpose of adjusting applicability. The ink in which the viscosity, the leveling properties and so forth are adjusted is prepared by dissolution of a polymerizable liquid crystal compound (or its composition), a photopolymerization initiator, a surfactant and so forth in an organic solvent when a film having optical anisotropy is produced from a polymerizable liquid crystal compound (or its composition). The ink is applied to a transparent substrate film aligned, the solvent is dried, and then the polymerizable liquid crystal compound (or its composition) is oriented. Next, the compound is polymerized with ultraviolet irradiation or heat and the aligned state is fixed. However, the compounds disclosed in non-patent documents Nos. 1 and 2 have subjects that should be solved in view of environmental load and safety (mutagenicity and toxicity), wherein solubility in an organic solvent such as propylene glycol monoethyl ether acetate (PGMEA) that is highly safe is low and thus a suitable concentration of the ink can not be achieved.
Conventional compounds are disclosed in the following patent documents: No. 1, JP H07-017910 A (1995) and No. 2, JP H09-316032 A (1997).
Conventional compounds are also disclosed in the following non-patent documents: No. 1, Polymer Chemistry, 1993, 31(9), 2249-60 and No. 2, Polymer, 1994, 35(3), 622-9.